Optimized approach for naphthalene wastewater biodegradation by Enterobacter ludwigii NS12 isolated from petroleum industry sludge: Bioreactor study and kinetic investigation

Environmental pollution resulting from industrialization has become a global concern in recent decades. The petroleum industry plays a crucial role in meeting the rising energy demands of rapidly growing sectors such as agriculture and pharmaceuticals [1]. However, oil spillage during crude oil drilling/extraction poses a significant challenge within this industry. This leads to the release of contaminants like oily sludge, volatile organic compounds (VOCs), polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons (PAHs) compounds into the environment [2,3]. In 2010, British Petroleum's Deepwater Horizon rig failure caused the largest United States (US) oil spill, releasing 4.9 million barrels, 3.9 % PAHs into the Gulf of Mexico [4,5]. Abdulla et al. [6] study on marine sediment in Qatar revealed variable concentrations of aliphatic and PAHs, with higher levels observed near oil and gas production sites, highlighting localized pollution concerns. According to “Drinking Water Hygienic Standards” of China (GB5749–2006, China), the total amount of PAHs exceeding 2 μg/L will threaten human health [7] Polyaromatic hydrocarbons including naphthalene have raised concerns over the past century regarding their detrimental effects on both marine and terrestrial ecosystems [8,9].

Naphthalene is a significant PAHs compound and finds extensive applications in the manufacturing of carbamate insecticides, phthalic anhydride, surface active agents, resins synthetic tanning agent, and color intermediary etc. [10]. The major pathways through which naphthalene enters the environment include crude oil, oily sludge, oil spills, and discharge of industrial wastewater effluent. The National Institute for Occupational Safety and Health (NIOSH) recommends an airborne exposure limit (REL) of 10 ppm (ppm) averaged over a 10-h workshift, with a ceiling of 15 ppm not to be exceeded during any 15-min work period [11]. Environmental Protection Agency (EPA) categorizes naphthalene as a Group C carcinogen for humans [10]. In addition to being carcinogenic, naphthalene can cause hemolytic anemia, and liver damage etc. through skin contact, ingestion, inhalation [12]. Hence, immediate action is necessary to address the naphthalene contamination in the environment. Several physico-chemical processes, such as adsorption, extraction, membrane separation, coagulation, and fenton oxidation, have been used for naphthalene treatment [[13], [14], [15], [16], [17], [18]]. However, these methods are expensive and generate toxic byproducts. To overcome these drawbacks, biodegradation has emerged as the most cost-effective and efficient method for remediation of naphthalene contamination in water [[17], [18], [19]]. In the past, biodegradation of PAHs was thought to have little practical use due to its persistent nature. Bioremediation of PAHs has been considered as a potential strategy as it actively participates in the complete breakdown of several pollutants to bacterial biomass, water, and carbon dioxide. The environmental impacts of these contaminants are comparatively lesser [10]. Naphthalene has been biodegraded by aerobic bacteria, with various pathways and metabolic diversities [20] Various microorganisms, including Pseudomonas, Rhodococcus sp., Sphingomonas sp., Halomonas sp., Stenotrophomonas sp., Bacillus sp., Sphingomonas sp., Mycobacterium sp., Micrococcus sp., and Marinobacterium sp. have been identified for their ability to degrade naphthalene [[19], [20], [21]].

Sonwani et al. [22] documented the biodegradation of naphthalene with Bacillus cereus RKS4, isolated from activated sludge sourced from the petroleum industry. In a comparable investigation, Rabani et al. [23] observed the degradation of naphthalene using Bacillus licheniformisand Bacillus sonorensis, isolated from sites contaminated by petroleum. Additionally, Gupta et al. [24] isolated and characterized bacterial strains from contaminated soil, identifying species belonging to Pseudomonas and Enterobacter sp., which exhibited potential for naphthalene degradation.

Due to limited substrate accessibility to the microbial community, many bacterial species exhibit slow degradation rates for naphthalene [[25], [26], [27]]. In recent years, variable factors such as pH, temperature and initial naphthalene concentration have been shown to affect naphthalene biodegradation during microbial remediation [28,29] To accelerate naphthalene biodegradation rates, researchers have turned to bioreactor systems. However, limited research is available on the utilization of such systems for the breakdown of naphthalene using potentially effective strains. Collina et al. [30] conducted a study in slurry-phase bioreactor on naphthalene biodegradation by Pseudomonas putida M8. Another investigation by Karamanev and Margaritis [31] explored the application of an airlift bioreactor for degrading petroleum hydrocarbons using immobilized cells. Due to the scarcity of literature on naphthalene biodegradation by indigenous strains in bioreactors, this study focuses on addressing this gap. The main purpose of this work is to study naphthalene biodegradation in bioreactor utilizing indigenous identifying Enterobacter ludwigii NS12 isolated from petroleum waste. This research offers novel insights into parameter optimization, growth kinetics, and metabolite identification to confirm naphthalene biodegradation, thereby advancing our comprehension of microbial degradation processes.

The findings of this research work emphasize real-time applications in bioremediation, highlighting a sustainable solution for effectively removing naphthalene contaminants from petroleum waste sites. Through substrate-specific analysis and deeper insights into the capabilities of indigenous Enterobacter ludwigii NS12, this study offers a promising approach for remediation strategies. Moreover, the investigation of kinetic parameters aids in the development of scalable processes, while metabolism and enzyme studies provide valuable insights into the biodegradation mechanisms, thus contributing to the advancement of practical and eco-friendly solutions for environmental cleanup initiatives.